From: Michal Hocko <mhocko@kernel.org>
To: Pavel Machek <pavel@ucw.cz>
Cc: linux-mm@kvack.org, Mel Gorman <mgorman@suse.de>,
Matthew Wilcox <willy@infradead.org>,
Vlastimil Babka <vbabka@suse.cz>, Neil Brown <neilb@suse.de>,
Theodore Ts'o <tytso@mit.edu>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] treewide: remove GFP_TEMPORARY allocation flag
Date: Mon, 28 Aug 2017 14:35:42 +0200 [thread overview]
Message-ID: <20170828123542.GJ17097@dhcp22.suse.cz> (raw)
In-Reply-To: <20170825213936.GA13576@amd>
On Fri 25-08-17 23:39:36, Pavel Machek wrote:
> On Fri 2017-08-25 10:04:42, Michal Hocko wrote:
> > On Fri 25-08-17 09:28:19, Pavel Machek wrote:
> > > On Fri 2017-08-25 08:35:46, Michal Hocko wrote:
> > > > On Wed 23-08-17 19:57:09, Pavel Machek wrote:
> > [...]
> > > > > Dunno. < 1msec probably is temporary, 1 hour probably is not. If it causes
> > > > > problems, can you just #define GFP_TEMPORARY GFP_KERNEL ? Treewide replace,
> > > > > and then starting again goes not look attractive to me.
> > > >
> > > > I do not think we want a highlevel GFP_TEMPORARY without any meaning.
> > > > This just supports spreading the flag usage without a clear semantic
> > > > and it will lead to even bigger mess. Once we can actually define what
> > > > the flag means we can also add its users based on that new semantic.
> > >
> > > It has real meaning.
> >
> > Which is?
>
> "This allocation is temporary. It lasts milliseconds, not hours."
And why would such a semantic make any sense what so ever? We certainly
do not try to wait for a pinned memory for $TIMEOUT when somebody really
needs a larger memory block and there is a temporary allocation standing
in the way. We simply do not know that an object is a temporary one.
> > > You can define more exact meaning, and then adjust the usage. But
> > > there's no need to do treewide replacement...
> >
> > I have checked most of them and except for the initially added onces the
> > large portion where added without a good reasons or even break an
> > intuitive meaning by taking locks.
>
> I don't see it. kmalloc() itself takes locks. Of course everyone takes
> locks. I don't think that's intuitive meaning.
I was talking about users of the flag. I have seen some to take a lock
right after they allocated GFP_TEMPORARY object.
> > Seriously, if we need a short term semantic it should be clearly defined
> > first.
>
> "milliseconds, not hours."
>
> > Is there any specific case why you think this patch is in a wrong
> > direction? E.g. a measurable regression?
>
> Not playing that game. You should argue why it is improvement. And I
> don't believe you did.
Please read the whole changelog where I was quite verbose about how the
current flag is abused and how its semantic is weak and encourages a
wrong usage pattern. Moreover it is not even clear whether it helps
anything. I haven't seen any actual counter argument from you other than
"milliseconds not hours" without actually explaining how that would be
useful for any decisions done in the core MM layer.
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2017-08-28 12:35 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-28 9:19 [RFC PATCH] treewide: remove GFP_TEMPORARY allocation flag Michal Hocko
2017-07-28 9:52 ` Mel Gorman
2017-07-28 10:27 ` Michal Hocko
2017-07-28 10:59 ` Mel Gorman
2017-07-28 13:15 ` Vlastimil Babka
2017-08-23 17:57 ` Pavel Machek
2017-08-25 6:35 ` Michal Hocko
2017-08-25 7:28 ` Pavel Machek
2017-08-25 8:04 ` Michal Hocko
2017-08-25 21:39 ` Pavel Machek
2017-08-26 4:11 ` NeilBrown
2017-08-28 12:36 ` Michal Hocko
2017-08-31 9:07 ` Pavel Machek
2017-08-31 9:29 ` Mel Gorman
2017-08-28 12:35 ` Michal Hocko [this message]
2017-08-31 9:10 ` Pavel Machek
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